We propose to extend the recently developed technique of supersonic jet spectroscopy to large biologically important molecules. The technique allows one to observe the optical spectra of isolated gas phase molecules whose internal degrees of freedom have been greatly cooled. The cooling greatly simplifies the spectrum and increases the effective spectral resolution. The specific class of molecules to be studied are the porphyrins and related molecules such as the phthalocyanines. With the increased resolution of supersonic jet spectroscopy, the vibronic structure of the gas phase spectrum is easily resolved, and we propose to study the effect of vibronic coupling (in particular the Jahn-Teller effect) in isolated orbitally degenerate states of metal porphyrins. We also propose to study the dynamics of intramolecular energy transfer in the porphyrins by exciting a single vibronic level and observing in the fluorescence spectrum the vibrational modes that are populated by energy transfer from the initially excited mode. Finally, we intend to develop two non-fluorescent means of detection, multiphoton ionization and coherent anti-Stokes Raman scattering (CARS) to allow supersonic jet spectroscopy to be extended to non-fluorescent biomolecules. The development of these techniques is intended to provide not only a very powerful new tool for the study of the properties of biomolecules, but also a very sensitive and specific analytical method for the detection of trace quantities of biologically important materials.